It is well known that an aromatic primary amine color developing agent as oxidized with an oxidizing agent of an exposed silver halide reacts with a coupler to give indophenol, indaniline, indamine, azomethine, phenoxazine, phenazine or similar dyes to thereby form a color image.
For forming magenta color images, 5-pyrazolone, cyanoacetophenone, indazolone, pyrazolobenzimidazole or pyrazolotriazole couplers are employed.
Almost all the magenta couplers which have hitherto been studied and used in practice are 5-pyrazolone compounds. However, it has been known that the dyes derived from 5-pyrazolone couplers have some unfavorable absorption in the vicinity of 430 nm to cause color contamination.
In order to overcome the problem or to provide couplers capable of forming magenta color images which have little absorption in the yellow color range, British Patent 1,047,612 has proposed pyrazolobenzimidazole skeletons, and U.S. Pat. No. 3,725,067 pyrazolo[5,1-c]-1,2,4-triazole skeletons.
The present inventors have developed magenta couplers capable of forming color images with little yellow absorption and having a good color forming capacity, which are pyrazoloazole magenta couplers of imidazo[1,2-b]pyrazoles, pyrazolo[1,5-b][1,2-4]triazoles, pyrazolo[1,5-d]tetrazoles, pyrazolo[1,5-d]benzimidazoles or pyrazolopyrazoles.
However, it has been found that the azomethine dyes formed from the pyrazoloazole couplers have a relatively low fastness to light and the poor light-fastness of the dyes could not be improved sufficiently by conventional color image stabilizers (for example, alkyl-substituted hydroquinones) which have heretofore been employed generally.
In order to overcome the problem, therefore, addition to various compounds has been tried so as to improve the light-fastness of the dyes. For example, JP-A-59-125732, JP-A-60-262159, JP-A-61-282245, JP-A-62-244045, JP-A-62-244046, JP-A-62-273531, JP-A-61-158330, JP-A-63-95439, JP-A-63-95448, JP-A-63-95450 and JP-A-63-284548 have proposed addition of alkoxybenzene derivatives. (The term "JP-A" as used herein means an "unexamined published Japanese patent application".) The compounds disclosed in these Japanese patent applications have an excellent light-fastness improving effect on the dyes derived from the couplers only in the range of high color density (hereinafter referred to as the "high density range").
In general, the dyes to be formed from pyrazoloazole couplers have an extremely poor light-fastness, especially in the range of low color density (hereinafter referred to as the "low density range"), which is unfavorable in view of the color balance with other color dyes.
Since addition of the above-mentioned dialkoxybenzene derivatives is insufficient to improve the light-fastness in the low density range, a technique for solving this problem is strongly desired.
JP-B-48-32728 (the term "JP-B" as used herein means an "examined published Japanese patent application") and JP-A-62-186263 and EP-A-309957 have proposed addition of phosphite esters to color photographic materials.
The compounds illustrated in the former two patent applications are effective for inhibiting yellow stains derived from couplers under heat or wet heat, but they often worsen the photographic characteristics of photographic materials by, for example, increasing fog or causing fluctuation of the sensitivity when the materials are color-developed. In addition, when the storage period from the manufacture of photographic materials to the use thereof is long, these effects become extremely noticeable. JP-A-62-186263 has proposed employment of metal complexes optionally along with alkoxybenzene derivatives. However, while addition of metal complexes improves the light-fastness, it increases the appearance of unfavorable yellow stains. Where dialkoxy benzene derivatives are added along with metal complexes, the light-fastness is somewhat improved, but the generation of unfavorable yellow stains is practically unavoidable. Therefore, addition of dialkoxybenzene derivatives is not practical. EP-A-309957 has proposed addition of tri-valent phosphorus compounds having a particular structure, which could improve the drawback of causing fog and sensitivity fluctuation but could not satisfactorily improve the color-fastness.
Given this situation, a technique for improving the color-fastness of the color dyes formed from couplers without causing any undesirable influence on the photographic properties of photographic materials and, in particular, of inhibiting fading of the color dyes in the low density range, has been desired.